Question 59 : How can you print leaf nodes of binary tree?

 Steps for counting number of leaf nodes are:

• If node is null then return 0
• If encounterd leaf node(i.e. node.left is null and node.right is null) then print the node.
• Recursively visit leaf subtree and right subtree.

Code for recursion will be:

 // Recursive Solution
    // print leaf nodes
    public static void printLeafNodes(TreeNode node) {
 
        if(node==null)
            return;
 
        if(node.left == null && node.right == null) {
            System.out.printf("%d ",node.data);
        }
        printLeafNodes(node.left);
        printLeafNodes(node.right);
    }

Example:
Binary tree:

Let's create java program for counting the number of leaf nodes:

public class BinaryTreePrintLeafNodes {
 
    public static class TreeNode
    {
        int data;
        TreeNode left;
        TreeNode right;
        TreeNode(int data)
        {
            this.data=data;
        }
    }
 
    // Recursive Solution
    // print leaf nodes
    public static void printLeafNodes(TreeNode node) {
 
        if(node==null)
            return;
 
        if(node.left == null && node.right == null) {
            System.out.printf("%d ",node.data);
        }
        printLeafNodes(node.left);
        printLeafNodes(node.right);
    }
 
    public static void main(String[] args)
    {
        // Creating a binary tree
        TreeNode rootNode=createBinaryTree();
        System.out.println("Printing leaf nodes in binary tree :");
        printLeafNodes(rootNode);
    }
 
    public static TreeNode createBinaryTree()
    {
 
        TreeNode rootNode =new TreeNode(40);
        TreeNode node20=new TreeNode(20);
        TreeNode node10=new TreeNode(10);
        TreeNode node30=new TreeNode(30);
        TreeNode node60=new TreeNode(60);
        TreeNode node50=new TreeNode(50);
        TreeNode node70=new TreeNode(70);
 
        TreeNode node5=new TreeNode(5);
        TreeNode node55=new TreeNode(55);
 
        rootNode.left=node20;
        rootNode.right=node60;
 
        node20.left=node10;
        node20.right=node30;
 
        node60.left=node50;
        node60.right=node70;
 
        node10.left=node5;
        node50.right=node55;
        return rootNode;
    }
}

Run above program and you will get following output:

Printing leaf nodes in binary tree :
5 30 55 70

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